Conventionally and in general, cutting tools include an indexable insert which is detachably attached to a tip portion of a cutting tool in order to perform a turning or planing operation for a workpiece such as made of various steels or cast irons, a drill or a micro drill which is used for performing a drilling operation for a workpiece as mentioned above, and a solid type end mill which is used for performing a face milling operation, a groove milling operation, or a shoulder milling operation for a workpiece as mentioned above. In addition, an indexable type end mill is also known, to which an indexable insert is detachably attached to a body for performing a cutting operation as in the case of the solid type end mill.
Moreover, conventionally and in general, as the coated cutting tools as mentioned above, a coated hard metal tool is known in which a hard coating layer, which has an average thickness of 0.5 to 10 μm and is made of, for example, titanium nitride (hereinafter termed TiN), titanium carbonitride (hereinafter termed TiCN), or a nitride compound (hereinafter termed (Ti, Al)N) layer that includes Al and Ti, is formed on a surface of a substrate made of a tungsten carbide (hereinafter termed WC) based cemented carbide, a titanium carbonitride (hereinafter termed TiCN) based cermet, or a cubic boron nitride (hereinafter termed c-BN) based sintered material (hereinafter such a substrate is referred to as a hard substrate). It is also well known that such a coated cutting tool is used in a continuous cutting operation or an interrupted cutting operation for various kinds of steels and cast irons.
As disclosed, for example, in Japanese Unexamined Patent Application, First Publication, No. S62-56565, it is known that the (Ti, Al)N layer as a hard coating layer for the aforementioned coated cutting tool is formed using a physical vapor deposition method in which an arc ion plating apparatus schematically shown in FIG. 2 is used, the inside of the apparatus is heated to a temperature of, for example, 500° C. using a heater, an electric current of, for example, 90A is made to flow as an arc discharge between an anode electrode and a cathode electrode (an evaporation source) to which a Ti—Al alloy piece having a predetermined composition depending on a desired coated layer composition is attached, a nitrogen gas as a reaction gas is simultaneously introduced into the apparatus so as to prepare a reaction atmosphere at, for example, 3 Pa, and on the other hand, a bias voltage of −200 V is applied to the hard substrate.
Among the aforementioned conventional coated cutting tools, a coated cutting tool in which a TiN layer is coated on a surface of a substrate exhibits a superior tool life when it is used for a cutting operation under a normal condition; however, the tool life of the coated cutting tool tends to end in an extremely short period due to excessive wear when it is used for a cutting operation under a high speed condition. Because a coated cutting tool, in which a TiCN layer or a (Ti, Al)N layer is coated, preferably, a (Ti, Al)N layer is coated, exhibits a superior wear resistance even when it is used for a cutting operation under a high speed condition due to an improved high temperature hardness and oxidation resistance of the (Ti, Al)N layer, it is known that the TiCN layer or the (Ti, Al)N layer is now widely used as a hard coating layer for coated cutting tools.
Moreover, in order to further improve the oxidation resistance and high temperature properties of the (Ti, Al)N layer, as disclosed, for example, in Japanese Unexamined Patent Application, First Publications, Nos. H07-310174, H08-199338, H09-295204, and H11-131215, it is known that various (Ti, Al, X)N layers can be formed using a physical vapor deposition method, which include a third metal, such as Si, Y, Zr, V, Nb, or Cr, in the form of replacing Ti and/or Al. Among these layers, it is known that oxidation resistance is significantly improved, in particular, in a nitride compound (hereinafter termed (Ti, Al, Si)N) layer to which Si is added so as to includes Ti, Al, and Si, and which satisfies a composition formula of (Ti1−(x+y)AlxSiy)NzC1-z) (where “x” indicates an atomic ratio of 0.05 to 0.75, “y” indicates an atomic ratio of 0.01 to 0.1, and “z” indicates an atomic ratio of 0.6 to 1), or in a nitride compound (hereinafter termed (Ti, Al, Y)N) layer to which Y is added so as to includes Ti, Al, and Y, and which satisfies a composition formula of (TiaAlbYc)CxN1−x) (where “a” indicates an atomic ratio of 0.3 to 0.7, “b” indicates an atomic ratio of 0.3 to 0.7, “c” indicates an atomic ratio of 0.01 to 2, and “x” indicates an atomic ratio of 0 to 1), and it is also known that a coated cutting tool in which the (Ti, Al, Si)N) layer having a significantly improved oxidation resistance is coated exhibits a superior cutting performance than a cutting tool having a (Ti, Al)N layer in a cutting operation, in particular, for a hard steel.
Furthermore, another coated cutting tool has been proposed, in which a hard coating layer, which has an average thickness of 1 to 15 μm and is made of a nitride compound (hereinafter termed (Ti, Al, Zr)N) layer that includes Ti, Al, and Zr and satisfies a composition formula of (Ti1−(X+Y)AlXZrY)N (where X indicates an atomic ratio of 0.45 to 0.65, and Y indicates an atomic ratio of 0.01 to 0.15), is formed on the surface of the aforementioned hard substrate using a physical vapor deposition method. It is also known that such a coated cutting tool is used in a high speed continuous cutting operation or in a high speed interrupted cutting operation for various kinds of steels and cast irons in which a significant amount of heat is generated because the aforementioned (Ti, Al, Zr)N layer forming the hard coating layer has a superior high temperature properties (high temperature hardness, heat resistance, and high temperature strength).
Moreover, it is also known that the aforementioned coated cutting tool is fabricated through a method in which the aforementioned hard substrate is mounted in, for example, an arc ion plating apparatus schematically shown in FIG. 2, which is a type of physical vapor deposition apparatus, an electric current of, for example, 90A is made to flow as an arc discharge between an anode electrode and a cathode electrode (an evaporation source) to which a Ti—Al—Zr alloy piece having a predetermined composition is attached under the conditions in which the inside of the apparatus is heated to a temperature of, for example, 400° C. using a heater, a nitrogen gas as a reaction gas is introduced into the apparatus so as to prepare a reaction atmosphere at, for example, 2 Pa, and on the other hand, a DC bias voltage of −200 V is applied to the aforementioned hard substrate, so that a hard coating layer, which is made of a (Ti, Al, Zr)N layer is formed on the surface of the aforementioned hard substrate.
In recent years, cutting operation apparatuses tend to have significantly high performance, and on the other hand, it is strongly demanded that cutting operations be performed using lower power and less energy at lower cost. Accordingly, a coated cutting tool is strongly demanded, which exhibits not only a superior cutting performance during high speed cutting operations for various kinds of steels and cast irons in which a significant amount of heat is generated, but also a superior cutting performance during a cutting operation for various kinds of steels and cast irons under severe cutting conditions, such as with a large depth of cut or a large feed.
On the other hand, a coated cutting tool in which the aforementioned (Ti, Al)N layer, (Ti, Al, Si)N, or (Ti, Al, Zr)N is coated on a surface of a substrate exhibits a superior wear resistance when it is used for a cutting operation under a high speed condition; however, the cutting tool tends to easily chip and the tool life of the coated cutting tool tends to end in a relatively short period when it is used for high speed cutting operations under severe cutting conditions, such as with a large depth of cut or a large feed.